1. Field of the Invention
The present invention relates to a process and an apparatus for implementing the said process for manufacturing composite sheets. It also relates to the composite products obtained.
2. Discussion of the Background
It is already known to manufacture composite sheets, in the form of panels or curved components, from fabrics formed both from reinforcing yarns and from thermoplastic yarns, by stacking the fabrics and then hot-pressing the stack thus formed, as described in Certificate of Utility FR 2,500,360. Such a process has, in particular, the disadvantage of being a batch process.
Moreover, the patent application filed in France under the filing number 96/00578 describes the manufacture of composite sheets from glass/organic material fabrics which are deposited continuously on a conveyor and then preheated in a hot-air oven before being introduced into a "belt press" (of the type described in Patent U.S. Pat. No. 4,277,539) where they are successively heated and cooled, while at the same time being compressed. Such a process is quick and can be used to obtain sheets suitable for moulding and having good mechanical properties.
However, on some of these sheets, defects are observed in the alignment of the glass filaments (presence of corrugations) in the longitudinal direction (direction of advance of the conveyor) or in the transverse direction, these defects being due to poor reorganization of the yarns after the preheating step and to the transverse shrinkage of the fabrics after this same step. These defects, which in many applications are not of great significance, may nevertheless not be desirable in certain very specific applications (especially in the manufacture of large flat thermoformed articles such as materials-handling boards, food trays, etc., where the filament alignment defects may be the cause of deformations within the articles).